Vacuum System

ABSTRACT

A vacuum system for use in excavation operations. The system uses a tank having an open end that is closed by a door. The door is opened and closed by a door lifting assembly made up of an upper linkage arm, a lower linkage arm and a hydraulic cylinder. A socket is formed in the upper linkage arm, and a shaft housing is formed in the lower linkage arm. The shaft housing engages with the socket to latch the door closed. The upper linkage arm is attached to the door at a first pivot axis and is attached to the lower linkage arm at a second pivot axis. The lower linkage arm is attached to a side of the tank at a third pivot axis. When the door is open, the second pivot axis extends below a reference plane that contains the first and third pivot axis.

SUMMARY

The present invention is directed to a vacuum system. The vacuum systemcomprises a tank having an open end, a closed end, and a first sidehaving a stub attached to and projecting out therefrom, a door used toclose the open end of the tank, and a door lifting assembly. The doorlifting assembly comprises an upper linkage arm, a lower linkage arm,and a hydraulic cylinder. The upper linkage arm has a first endconnected to an outer surface of the door and a second end. The upperlinkage arm further comprises a socket disposed between the first endand the second end. The lower linkage arm has a first end and a secondend. The lower linkage arm further comprises a stub housing disposedbetween the first end and the second end through which the stub isreceived. The hydraulic cylinder is connected to the second end of thelower linkage arm. Activation of the hydraulic cylinder causes thesocket on the upper linkage arm to engage with the stub housing disposedin the lower linkage arm.

The present invention is also directed to a lifting mechanism foropening a vacuum tank. The vacuum tank comprises a door and a tank Thelifting mechanism comprises an upper linkage arm, a lower linkage armand a hydraulic cylinder. The upper linkage arm has a first endpivotally secured to the door at first pivot axis and a second end. Thelower linkage arm has a first end and a second end and comprises asecond pivot axis disposed between the first end and the second end. Thelower linkage arm is pivotally secured to a first side of the tank atthe second pivot axis, and the first end of the lower linkage arm ispivotally secured to the second end of the upper linkage arm at a thirdpivot axis. The hydraulic cylinder is connected to the second end of thelower linkage arm. The first pivot axis and the second pivot axis are ona first plane when the linkage arm are fully extended and the door is inan open position, and the third pivot axis is beneath the first planewhen the linkage arms are fully extended and the door is in an openposition.

The present invention is further directed to an apparatus comprising atank having an open end and carrying an externally projecting shafthaving a shaft axis, a door hingedly mounted at the tank's open end andmovable between open and closed positions, and an elongate lower armsupported by the tank and rotatable about the shaft axis. The apparatusfurther comprises an elongate upper arm pivotally secured to the door ata first pivot axis and pivotally secured to the lower arm at a secondpivot axis spaced from the first pivot axis. The second pivot axis ofthe lower arm crosses a reference plane as the door approaches its openposition. The reference plane contains both the shaft axis and the firstpivot axis.

The present invention is even further directed to an apparatuscomprising a tank having an open end and carrying an externallyprojecting shaft, a door hingedly mounted at the tank's open end andmovable between open and closed positions, and an elongate lower armhaving a shaft housing through which the shaft extends. The apparatusfurther comprises an elongate upper arm pivotally secured to the door ata first pivot axis and pivotally secured to the lower arm at a secondpivot axis spaced from the first pivot axis. The second arm has a socketthat opens toward the first pivot axis and within which the shafthousing of the lower arm is at least partially positionable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first side of a vacuum system. Thevacuum system comprises a tank having a door closing its open end. Thedoor is shown in a closed position.

FIG. 2 is a perspective view of the vacuum system of FIG. 1 showing theopposite second side of the system with the door in the closed position.

FIG. 3 is a side view of the vacuum system of FIG. 2.

FIG. 4 is a perspective view of a first side of the tank. The tank isremoved from vacuum system and the door is in the closed position.

FIG. 5 is a side view of the first side of the tank. The tank is removedfrom vacuum system and the door is in the closed position.

FIG. 6 is a side view of the first side of the tank. The tank is removedfrom vacuum system and the door is in a fully opened position.

FIG. 7 is a side view of the first side of the tank. The tank is removedfrom vacuum system and the door is approximately halfway between theopen and closed position.

FIG. 8 is a close up view of a door lifting assembly on the first sideof the tank. An upper linkage arm of the door lifting assembly is shownstarting to engage with a lower linkage arm as the door is closing. Anouter member of the lower linkage arm has been removed to better showthis engagement.

FIG. 9 is the view of FIG. 8 with the upper linkage arm further engagedwith the lower linkage arm as the door is further closed.

FIG. 10 is the view of FIG. 9 with the upper linkage arm fully engagedwith the lower linkage arm and the door is fully latched and in theclosed position.

FIG. 11 is a partially exploded view of the tank. The first side of thetank is shown. The tank is removed from the vacuum system and the firstlinkage assembly and a second linkage assembly are shown in an explodedfashion. The door is shown removed from the tank to expose an interiorof the tank.

FIG. 12 is a perspective view of a first side of an alternativeembodiment of the vacuum system.

FIG. 13 is a perspective view of a second side of the alternativeembodiment of the vacuum system shown in FIG. 12.

DETAILED DESCRIPTION

With reference to FIGS. 1-3, a vacuum system 10 is shown supported on atrailer 12. The vacuum system 10 may also be supported on a truck. Thevacuum system 10 may be used to assist in excavation or clean-upoperations. The vacuum system 10 comprises a tank 14, a power source 16,a vacuum pressure system 18, and a vacuum hose 20. The tank 14 will bediscussed first herein and the remaining components of the system iowill be described later on in this application.

As shown in FIGS. 1-3, the tank 14 is generally cylindrical and has anopen end 22 and a closed end 24. The open end 22 of the tank 14 isclosed by a door 26.

The door 26 is shown in a closed position in FIGS. 1-3. A first doorlifting assembly or lifting mechanism 28 is used to open and close thedoor 26.

Turning now to FIGS. 4-5, the tank 14 is shown in more detail. The door26 is shown in the closed position in FIGS. 4-5. The door 26 isgenerally circular and dome shaped having an apex at its center. Theouter periphery of the door 26 terminates at an edge 30. The edge 30 ofthe door 26 seals against a sealing flange 32 formed around the outercircumference of the open end 22 of the tank 14.

The door 26 is pivotally supported on the tank 14 with a hinge 34. Thehinge 34 comprises a tank bracket 36 that is attached to a top 38 of thetank 14 at its open end 22. The tank bracket 36 comprises two parallelplanar members 40. Each planar member 40 has a tab 42 that projects pastthe open end 22 of the tank 14. The hinge 34 further comprises a doorbracket 44 that is attached to the door 26 adjacent the top 38 of thetank 14. The door bracket 44 has two parallel planar arms 46 that extendupwards past the edge 30 of the door 26. The arms 46 are rigidlyconnected via a cross-bar 48. The cross-bar 48 is disposed through apair of slots 50 formed in the tabs 42 of the tank bracket 36. Thecross-bar 48 may pivot within the slots 50 such that the door 26 pivotsrelative to the tank 14. The slots 50 are wider than the width of thecross-bar 48. This allows the door 26 to move slightly toward and awayfrom the open end 22 of the tank 14 as it is opened and closed.

The door 26 is opened and closed using the first door lifting assembly28. The first door lifting assembly 28 is attached to a first side 52 ofthe tank 14. A second door lifting assembly 54 is attached to a secondside 56 of the tank 14 (FIGS. 2-3). The lifting assemblies 28, 54 areconfigured to distribute the closing force applied to the door 26uniformly about the periphery of the door 26. An evenly distributedclosing force upon the door 26 helps to create a uniform seal around theperiphery of the tank 14. This helps to reduce the likelihood ofdimpling or deforming the door 26.

The lifting assemblies 28, 54 are each attached to the outer surface ofthe door 26 via a bracket 58 and a second bracket 60. The brackets 58,60 are attached to the opposite sides of the outer periphery of themiddle of the door 26. The brackets 58, 60 are an equal distance fromthe apex of the door 26. Each bracket 58, 60 comprises a mounting member62 that is attached to the outer surface of the door 26. Each bracket58, 60 further comprises a horizontal member 64 attached to the outersurface of the mounting member 62. The first door lifting assembly 28and the second door lifting assembly 54 work in concert to open andclose the door 26. The assemblies 28, 54 pull the door 26 closed bypulling on the brackets 58, 60. The brackets 58, 60 help distribute theclosing force uniformly around the periphery of the door 26.

The first door lifting assembly 28 comprises an elongate first upperlinkage arm 66, an elongate first lower linkage arm 68, and a firsthydraulic cylinder 70. The second door lifting assembly 54 is configuredidentically to the first door lifting assembly 28. The second doorlifting assembly 54 comprises an elongate second upper linkage arm 72,an elongate second lower linkage arm 74, and a second hydraulic cylinder76 (FIGS. 2-3). Simultaneous activation of the hydraulic cylinder 70 andthe second hydraulic cylinder 76 causes the arms 66, 68 and 72, 74 toextend or retract to open and close the door 26.

Continuing with FIGS. 4-5, a first end 78 of the upper linkage arm 66 ispivotally attached to the mounting bracket 58 via a pivot pin 80. Thepivot pin 80 coincides with a first pivot axis 82. A second end 84 ofthe upper linkage arm 66 is pivotally attached to a first end 86 of thelower linkage arm 68 via a pivot pin 88. The pivot pin 88 coincides witha second pivot axis 90.

The lower linkage arm 68 has a shaft or stub housing 92 formed betweenits first end 86 and second end 94. The stub housing 92 has an openingfor receiving a shaft or stub 96. The stub 96 is best shown in FIG. 11,which is an exploded view of the first door lifting assembly 28. Thestub 96 projects externally out from the first side 52 of the tank 14.The stub 96 supports the lower linkage arm 68 on the first side 52 ofthe tank 14. The stub housing 92 in the lower linkage arm 68 may pivotabout the stub 96. The stub 96 coincides with a shaft axis or thirdpivot axis 98.

The hydraulic cylinder 70 comprises a cylinder 100 and a piston 102. Thesecond end 94 of the lower linkage arm 68 is pivotally attached to theend of the piston 102 via a pivot pin 104. An externally projectingcylinder shaft 106 is also attached to the first side of the tank 14proximate its closed end 22. The cylinder shaft 106 is best shown inFIG. 11. A cylinder shaft housing 107 is formed at the end of thecylinder 100 for receiving the cylinder shaft 106. The hydrauliccylinder 70 is supported on the first side 52 of the tank 14 via thecylinder shaft 106.

Turning now to FIG. 6, the door 26 is shown in a fully opened position.

When the door 26 is fully open, the piston 102 is entirely retractedwithin the cylinder 100 and the arms 66, 68 are fully extended.Retraction of the piston 102 within the cylinder loo forces the arms 66,68 to extend upwards. The first pivot axis 82 and the third pivot axis98 are on the same reference plane. The reference plane is designated bydashed line 108. The second pivot axis 90 crosses the reference plane asthe door 26 is moved from the closed position to a fully openedposition. Once the door 26 is in the fully opened position, the secondpivot axis 90 is positioned beneath the reference plane or dashed line108. In this position, the door 26 is biased toward an open position orstate without the need for constant pressure from the hydraulic actuator70.

The second door lifting assembly 54 operates simultaneously andidentically as the first door lifting assembly 28 when the door 26 isopened. As discussed below, the second door lifting assembly 54 alsooperates simultaneously and identically as the first door liftingassembly 28 with the door is closed.

As shown in FIG. 6, the upper linkage arm 66 has a top surface no and abottom surface 112. A socket 114 is formed in the bottom surface 112 ofthe arm 66 between its first end 78 and second end 84. The socket 114opens towards a bottom 116 of the tank 14. The socket 114 has a boundaryhaving the shape of a circular arc. In one embodiment, the boundary maybe semi-circle. The boundary of the socket 114 has opposed first andsecond ends 118 and 120. A ramp 122 is formed between the second end 120and the bottom surface 112 of the upper linkage arm 66. The second upperlinkage arm 72 is configured identically to the upper linkage arm 66.

Turning back to FIG. 4, the lower linkage arm 68 comprises an innermember 124 and an outer member 126. This is also shown in FIG. 11. Thestub housing 92 is formed in both the inner and outer members 124, 126.The stub 96 is disposed through stub housing 92 formed in both the innerand outer member 124, 126. When the door 26 is in the closed position,as shown in FIG. 4, the upper linkage arm 66 may be positioned betweenthe inner and outer member 124, 126 of the lower linkage arm 68.

With reference now to FIGS. 7-10, the process of closing and latchingthe door 26 is shown in more detail. In FIGS. 8-10, the outer member 126of the lower linkage arm 68 has been removed to better show thisprocess. In FIG. 7, the piston 102 is partially extended from thecylinder 100. This causes the second pivot axis 90 to pivot upwardstowards the top 38 of the tank 14. As the second pivot axis 90 pivotsupwards, it pulls the first end 78 of the upper linkage arm 66downwards. This causes the upper linkage arm 66 to pull the door 26towards the open end 22 of the tank 14. As the piston 102 extendsfarther out of the cylinder 100, as shown in FIGS. 8-9, it forces thesecond pivot axis 90 to pivot downwards towards the cylinder 100. Thiscauses the arms 66, 68 to begin folding together.

Continuing with FIGS. 8-10, as the arms 66, 68 approach one another, theramp 122 on the upper linkage arm 66 starts to engage with the stubhousing 92 formed in the inner member 124 of the lower linkage arm 68.As the ramp 122 engages with the stub housing 92 the ramp 122 directsthe stub housing 92 into the socket 114. The door 26 is fully closed andsealed when the stub housing 92 is fully seated within the socket 114,as shown in FIG. 10.

Seating the stub housing 92 within the socket 114 locks the linkage arms66, 68 in place and pulls the door 26 toward the open end 22 of the tank14 with a force that is not generated by the hydraulic cylinder 70. Ifthe hydraulic cylinder 70 were removed from the first side 52 of thetank 14 when the stub housing 92 is seated within the socket 114, thedoor 26 would remain closed. The outer member 126 of the lower linkagearm 68 covers the connection between the stub housing 92 and socket 114when the door 26 is closed. This helps protect the connection from anyoutside debris during operation.

As shown in FIGS. 8-10, the second end 84 of the upper linkage arm 66comprises a slot 128 for receiving the pivot pin 88 at the second pivotaxis 90. The slot 128 allows the pivot pin 88 to move laterally at thesecond pivot axis 90. The lateral movement of the pivot pin 88 withinthe slot 128 allows the ramp 122 to direct the stub housing 92 into thesocket 114 to latch the door 26 closed.

Turning back to FIGS. 1-3, the overall vacuum system 10 is shown in moredetail. The power source 16 of the vacuum system 10 is supported on afront end 130 of the trailer 12. The tank 14 is supported on a rear end132 of the trailer 12 such that the door 26 of the tank 14 is accessibleat the rear end 132 of the trailer 12. The power source 16 may comprisean internal combustion engine or an electric motor. The power source 16is used to supply power to the various components of the system 10during operation.

The vacuum pressure system 18 is disposed on the side of the trailer 12adjacent the tank 14. The vacuum pressure system 18 is used to pull airfrom the tank 14 to create a vacuum within the tank. The vacuum createdin the tank 14 causes debris, including liquid and soil, to be pulledinto the tank 14 through the vacuum hose 20. The hose 20 is connected tothe top 38 of the tank 14 and supported on a boom 134. The boom 134 ispivotally connected to the tank 14 to allow an operator to swing thehose 20 to a desired location. In an alternative configuration the hose20 may be connected to the door 26 at an inlet 136.

A reservoir 138 is also supported on the trailer 12 between the powersource 16 and the tank 14. The reservoir 138 holds water that may beused to break up soil to be excavated by the vacuum system 10. Inoperation, water is pumped from the reservoir 138 and expelled from awater hose (not shown) at high pressure to break up the soil to beexcavated. The vacuum system 10 is then used to clear away the soil andwater mixture.

A tool carrier 140 may also be mounted to the trailer 12 beside the tank14.

The tool carrier 140 may be configured to store detachable portions ofthe hose 20 or other tools needed during excavation operations duringnon-use or transport of the system 10.

The tank 14 is supported on the trailer 12 with a mounting bracket 142.The mounting bracket 142 is rectangular in shape. The bottom 116 of thetank 14 sits down within and is secured to the bracket 142. The mountingbracket 142 is pivotally connected to the trailer 12 at connector points144. The connector points 144 are below the open end 22 of the tank 14.

A hydraulic lifting assembly 146 is attached to the trailer 12 and thesides of the mounting bracket 142. When activated, the hydraulic liftingassembly 146 pivots the mounting bracket 142 forward at the connectorpoints 144. This pivoting motion causes the tank 14 to title downward.Pivoting the tank 14 in this manner allows contents to be dumped fromthe tank 14 when the door 26 is open. A gate valve 148 is also formed onthe door 26 proximate the bottom 116 of the tank 14. Contents may beremoved from the tank 14 by opening the gate valve 148 if the door 26 isin the closed position.

Turning now to FIGS. 4 and 11, a flange 150 is supported on the top 38of the tank 14. The flange 150 is configured for connection to thevacuum pressure system 18 to create a vacuum in the tank 14. A secondflange member 152 adjacent the flange 150 is also supported on the top38 of the tank 14. The second flange member 152 provides a base for theboom 134 and an inlet port for the hose 20. The second flange member 152may be used when the boom 134 is used to collect material into the tank14. A bracket or brackets 154 may also be supported on the tank 14proximate its closed end 24. The brackets 154 may be used to connectadditional components to the tank 14, such as hydraulics to operate theboom 134.

With reference now to the door 26, a sight glass 156 is formed at thecenter or apex of the door 26. The sight glass 156 permits an operatorto visually inspect the interior of the tank 14 when the door 26 isclosed. The door 26 may also comprise a second sight glass 158 disposedproximate the top 38 of the tank 14. When in-tank material becomesvisible through the second sight glass 158, an operator will know thatthe tank is nearly full. An L-shaped bracket 160 may also be attached tothe outer surface of the door 26 between the door bracket 44 and thesecond sight glass 158. The L-shaped bracket 160 may be configured tosupport reflectors or warning lights.

A flange 162 is also shown supported on the door 26 proximate the bottom116 of the tank 14. The flange 162 supports the gate valve 148. The gatevalve 148 allows for the removal of material and fluids from the tank 14without requiring the door 26 to be opened. The inlet 136 may bepositioned on the door 26 above the sight glass 156. The inlet 136 maybe connected to the vacuum hose 20. A vacuum air stream may be pulledthrough the inlet 136 if the boom 134 arrangement is not used. The inlet136 is closed off with a plug 164.

Referring now only to FIG. 11, an interior 166 of the tank 14 is shown.A support member 168 may be disposed across the center diameter of thetank 14 proximate its open end 22. The support member 168 may comprise apipe, a square tube member, or possibly an elongate member having anoval-shaped cross sectional profile. The support member 168 may besupported on brackets 170. The brackets 170 may also support the stub 96and a second stub 172 that project out from the first side 52 and thesecond side 56 of the tank 14. The support member 168 helps to maintainthe shape of the tank 14 by reducing the likelihood the tank will warpduring manufacture or use of the vacuum system 10. A pair of supportmembers 168 may also be used in lieu of a single support member. Onesupport member may be disposed above the center diameter of the tank 14and a second support member may be disposed below the center diameter ofthe tank.

Turning now to FIGS. 12-13, an alternative embodiment of the vacuumsystem 200 is shown supported on a trailer 201. The vacuum system 200comprises a tank 202, a power source 204, a vacuum pressure system 206,and a vacuum hose (not shown). The vacuum hose attaches to an inlet 207on a top 210 of the tank 202. The vacuum hose may be supported and movedaround on the articulating jib 212.

The power source 204 of the vacuum system 200 is supported on a frontend 214 of the trailer 201. The power source 204 is identical to thepower source 16. The tank 202 has a door 208 that closes an open end 213of the tank 202. The tank 202 is supported on a rear end 216 of thetrailer 201 such that the door 208 of the tank 202 is accessible at therear end 216 of the trailer 201.

The vacuum pressure system 206 is supported on the trailer 201 betweenthe power source 204 and a closed end 218 of the tank 202. The vacuumpressure system 206 comprises a hose 220 that is attached to an inlet224 at the top 210 of the tank 202. The vacuum pressure system 206 pullsair from inside of the tank 202 to create a vacuum within the tank 202.

A pair of reservoirs tanks 228 is supported on the trailer 201 onopposite sides of the tank 202. Like reservoir 138, the reservoir tanks228 hold water that may be used to break up soil to be excavated. Thevacuum system 200 is then used to clear away the soil and water mixture.

The tank 202 uses the same lifting mechanisms 28 and 54 as the tank 14to open and close the door 208. The door 208 is identical to door 26except that only one sight glass 230 is shown on the door 208. The sightglass 230 is positioned adjacent an alternative hose inlet 232. A pairof mounting brackets 234 is also shown attached to opposite sides of thedoor 202. Like mounting brackets 58 and 60, the mounting brackets 234are each attached to the lifting mechanisms 28 and 54. The mountingbrackets 234 are identical to mounting brackets 58 and 60 except thatmounting brackets 234 each further comprise a tool mount 236.

The tool mount 236 has a hook 238 and a notch 240. The hook 238 andnotch 24o may be used to support tools on the door 202. A latch 242 isalso attached to the tool mount 236. The latch 242 works to hold thetools in place on either the hook 238 or the notch 240 when the latch isin a latched position. The latch 242 is shown in a latched position inFIGS. 12-13. The latch 242 is held in place by a spring 244. The latch242 may be temporarily pulled outward by extending the spring and turnedgo degrees in order to place a tool on the hook 238 or in the notch 240.

Although the preferred embodiment has been described in detail, itshould be understood that various changes, substitutions and alterationscan be made therein without departing from the spirit and scope of theinvention as defined by the appended claims.

1. A vacuum system, comprising: a tank having an open end and a closedend; a door secured to the tank by a hinge and configured to close theopen end of the tank; and a door lifting assembly, comprising: a primarylinkage arm, having a first end and a second end, in which the first endis pivotally secured to the door at a first pivot axis; and a secondarylinkage arm, having a first end and a second end, in which the first endof the secondary linkage arm is pivotally secured to the second end ofthe primary linkage arm at a second pivot axis; in which the secondarylinkage arm is pivotally secured to a first side of the tank at a thirdpivot axis disposed between the first end and the second end of thesecondary linkage arm; and in which the second pivot axis is alwayspositioned intermediate the third pivot axis and the hinge.
 2. Thevacuum system of claim 1 in which a socket is formed in the primarylinkage arm between its first and second end.
 3. The vacuum system ofclaim 2 in which the socket is configured to engage with the secondarylinkage arm at the third pivot axis.
 4. The vacuum system of claim 1further comprising a hydraulic cylinder connected to the second end ofthe secondary linkage arm.
 5. The vacuum system of claim 4 in which thehydraulic cylinder comprises a piston and a cylinder, in which thelinkage arms are fully extended when the piston is retracted within thecylinder.
 6. The vacuum system of claim 1 in which the third pivot axiscomprises a stub attached to and projecting out from the first side ofthe tank and extending through a stub housing formed in the secondarylinkage arm for receiving the stub.
 7. The vacuum system of claim 1 inwhich the primary linkage arm and the secondary linkage arm are separatepieces.
 8. The vacuum system of claim 1 in which the second end of theprimary linkage arm comprises a slot for receiving a pivot pin, in whichthe slot allows for lateral movement of the primary linkage arm relativeto the pivot pin.
 9. The vacuum system of claim 1 in which the secondarylinkage arm comprises an inner member and an outer member and theprimary linkage arm is positionable between the inner member and theouter member.
 10. The vacuum system of claim 1 further comprising asupport member disposed across a center diameter of the tank, in which alongitudinal axis of the support member is spaced from the third pivotaxis.
 11. The vacuum system of claim 1 in which the first pivot axis,the second pivot axis, and the third pivot axis are positionable on aplane that includes the first pivot axis, the second pivot axis, and thethird pivot axis as the door moves from a closed position to an openposition.
 12. A vacuum system, comprising: a tank having an open end anda closed end; a movable door configured to close the open end of thetank; and a door lifting assembly, comprising: a first rigid linkelement having two and only two points for pivotal attachment,designated as first and second attachment points, the first link elementpivotally secured to the door at the first attachment point; a secondrigid link element having three and only three points for pivotalattachment, designated as a primary attachment point and first andsecond secondary attachment points, the second link element pivotallyattached to the second attachment point of the first link element at thesecond secondary attachment point, the second link element pivotallyattached to the tank at the primary attachment point, in which a minimumcentral angle defined by movement of the secondary attachment pointsabout the primary attachment point is greater than 90 degrees; and amotive power source pivotally attached to the first secondary attachmentpoint of the second link element.
 13. The vacuum system of claim 12 inwhich the minimum central angle is less than 180 degrees.
 14. The vacuumsystem of claim 12 in which the first attachment point of the first linkelement, the second secondary attachment point of the second linkelement, and the primary attachment point of the second link element arepositionable on a plane that includes said attachment points as the doormoves from a closed position to an open position.
 15. The vacuum systemof claim 14 in which the second secondary attachment point of the secondlink element is beneath the plane when the linkage arms are fullyextended and the door is in the open position.
 16. The vacuum system ofclaim 12 in which a socket is formed in the first link element betweenits first and second attachment points.
 17. The vacuum system of claim16 in which the socket is configured to engage with the second linkelement at the primary attachment point.
 18. The vacuum system of claim12 in which the primary attachment point comprises a stub attached toand projecting out from a side of the tank and extending through a stubhousing formed in the second link element for receiving the stub. 19.The vacuum system of claim 12 in which the first link element and thesecond link element are separate pieces.
 20. The vacuum system of claim12 further comprising a support member disposed across a center diameterof the tank, in which a longitudinal axis of the support member isspaced from the primary attachment point.